Monocytes are being characterized for the expression levels of CD40, CD80, CD86, CD120b, and the gamma interferon receptor alpha chain. These studies have identified two patients with gamma interferon receptor alpha chain deficiency, and the molecular level of this defect is being actively examined. In addition, one patient with interferon gamma receptor beta chain deficiency also has been characterized at the molecular level. As a consequence of these studies, an intracellular flow cytometric method for evaluating STAT protein phosphorylation has been developed and validated. This approach can be adapted for use for a wide variety of activation associated protein alterations. This line of investigation currently is being pursued.